Gases containing sulfur compounds and/or hydrogen cyanide are frequently encountered in industries wherein combustion furnaces are utilized. For example, the tail gas stream from a furnace carbon black production process generally contains carbon sulfides, such as carbon disulfide (CS.sub.2) and carbonyl sulfide (COS), and also contains hydrogen cyanide (HCN).
Often it is desirable to remove the sulfur containing species from the gas stream to comply with laws and regulations regarding the emission of the species into the atmosphere. CS.sub.2 and COS have a relatively inert chemical character and therefore can be difficult to remove from a gas stream. On the other hand, hydrogen sulfide (H.sub.2 S) may be readily removed from gas streams by a variety of processes. Sulfur in the form of carbon sulfides may be catalytically converted to H.sub.3 S; similarly, nitrogen fixed as HCN may be catalytically reacted to ammonia (NH.sub.3). Typical commercial catalysts for these conversions include titania (titanium dioxide), cobalt and molybdenum promoted alumina (cobalt oxide and molybdenum trioxide/aluminum oxide), supported platinum and chromium oxide promoted alumina. These typical commercial catalysts may be effective in the absence of oxygen. However, in the presence of even small (approximately 0.1% or greater) concentrations of oxygen in the feed gas stream, these materials lose their desired catalytic function. For example, in the presence of oxygen, promoted alumina catalysts become sulfated and lose catalytic activity. With titania catalysts, small concentrations of oxygen may lead to conversion of sulfur species to SO.sub.2 and/or COS, and poor carbon sulfide and HCN conversions.
In order to overcome the deletrious effects of oxygen on typically utilized catalysts, a dual stage catalyst bed has been suggested. For example, U.S. Pat. No. 4,981,661 discloses a two stage process wherein, in a first stage, oxygen is removed by hydrogenation and in a second stage the catalytic hydrolysis of carbon sulfides and HCN occurs. However, it would be advantageous to have a catalyst that would be effective for carbon sulfide and HCN conversion, even in the presence of oxygen, and therefore could be utilized in a single stage catalytic reactor.
It is an object of the present invention to provide novel catalysts. The catalysts are particularly effective for conversion of carbon sulfides and HCN, even in the presence of oxygen in concentrations up to 2% by volume (dry basis), preferably oxygen in concentrations up to 1.0% by volume, (dry basis). A further object of the present invention is a method for converting carbon sulfides and HCN of a gas stream utilizing the catalysts of the present invention.